Fix helper inclusion for Rails 5
Fix helper inclusion for Rails 5

Calling the `helper` method after upgrading to Rails 5 resulted in the
following error:

undefined method 'helper' for ActionController::API:Class

This commit follows the lead of the following commit on another project:
https://github.com/weppos/breadcrumbs_on_rails/commit/3a3ac0c0d42bb0535418942e9051d687661582e5

Ink/filepicker-rails,Ink/filepicker-rails,Ink/filepicker-rails